abci: fix rpc response deserialization

[yihuang]

Fix rpc response deserialization issues. fix #423

By the way, the null_as_default deserializer might be good to use on some other fields.

[xla]

Thanks for the concise change-set. Could you explain why the null as default behaviour is needed/desired and if it is treated like that somewhere else in tendermint like that.

[xla]

You can avoid all of these field attribute by putting a #[serde(rename_all = "camelCase")] on the struct. See the section in the container attribute documentation.

[yihuang]

I think the camelCase here is a special case, because other places tendermint actually use a_b format.

[yihuang]

Thanks for the concise change-set. Could you explain why the null as default behaviour is needed/desired and if it is treated like that somewhere else in tendermint like that.

• The "data":null, is what I observed from the response return from tendermint 0.33.6 (also other versions), I pasted that response here: rpc response decode failed with recent released version of tendermint #423 (comment)
• I don't know a proper spec on protobuf json format conversion, but from my understanding, protobuf don't distinguish between default value and non-exist ones(non-exist value can be skipped in wire message).
  So for example, Option<Vec<_>> might be simplified with a Vec<_> with null_as_default semantic.

[liamsi]

It be great, if this PR also comes with an (updated?) test-case. Note that currently, there is a test-failure:

---- endpoints::block_results stdout ----
thread 'endpoints::block_results' panicked at 'called `Result::unwrap()` on an `Err` value: Error { code: ParseError, message: "Parse error. Invalid JSON", data: Some("missing field `gasWanted` at line 34 column 7") }', rpc/tests/integration.rs:113:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[yihuang]

It be great, if this PR also comes with an (updated?) test-case. Note that currently, there is a test-failure:

The test case is fixed now.

[xla]

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